Reverse wiring transformer

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charlie said:
Why not? You are still changing the turns ratio. :confused:
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I had read that here on this forum, but I may be mistaken.

From Square D
Taps are on the designed primary side of a transformer to compensate for poor (other than nominal) incoming voltage, allowing the transformer to operate at it`s designed magnetic flux levels in the core. When backfeeding the transformer, the magnetic flux level in the core cannot be optimized. However, the output voltage provided by the taps can be used with care provided the current rating of the tap is not exceeded.
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iwire said:
. . . provided the current rating of the tap is not exceeded
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That is interesting, normally, the primary coil magnet wire is brought out to the tap changer or tap board and all of the tap wires or links are the same as the primary coil magnet wire. :-?
 
iwire,
you may have missed my comment regarding taps:"When using this transformer as a step down the taps are on the output sided. If you had (2)2-1/2% FCAN and (4)2-1/2%FCBN taps when the taps are on the output of the transformer you have 4 up and 2 down."
Yes the taps are alive and well when transformer is feed in either direction.
And, yes, when the guys wind transfomrers they do count turns as included on the winding sheet provided by the design engineer.
 
glene77is said:
Why would the turns ratio be 'a bit less' ?
What might be the purpose?
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Look at it like this, using, to make a simple example, a 120-12v transformer. It looks like a perfect 10:1 voltage ratio, which it is in theory. But in reality, it might have been wound to be a 10:1.1 ratio, to compensate for losses.

That means, with a perfect 120v supply and no line and heat losses, the output would be 13.2v. However, with the usual line losses, transformer losses, etc., the final output voltage would end out more like the desired 12v.

Now, let's say we want to use this transformer as a 12-120v unit. We apply 12v to the original secondary, and because of the 1.1:10 voltage ratio, the original primary would put out only 109v, and that's without any losses.
 
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gar said:
080913-1710 EST

Larry:

You have a slight typo. You meant 109, instead of 10.9 .

.
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I saw that too before Bob fixed it. :)

Roger
 
erichall1 said:
Thanks for all the replies.
The transformer is 45KVA. Will I be losing about half the KVA by backfeeding?
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Power in KVA is constant through the XFMR (with some loss due to hysteresis and eddy currents) regardless of the direction it is fed. Remember VA= Volts * Amps. For power, current is inversely proportional to potential.

Therefore, the answer to your question is no. Your XFMR will remain 45KVA.
 
080913-1909 EST

jeremysterling:

You are approximately correct, but the thermal problems based on where the primary and secondary are physically located will make a difference because of the I^2*R loss difference. Large transformers may be very efficient and there may be little difference. Small transformers will present a greater problem.

It would be necessary to run a maximum hot spot temperature measurement to determine if there was much difference.

.
 
A picture of Goofy may have been fitting but, a picture of "Tripod" didn't make a lot of sense.

goofy.jpg.w300h418.jpg


Roger
 
LarryFine said:
That's the picture I posted. Whar is "tripod?"
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I don't know whar tripod is but, as Bob says, a logo for Tripod is all we see.

Roger
 
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